Fixed abrasive pad having different real contact areas and fabrication method thereof

ABSTRACT

Disclosed is a method for fabricating a fixed abrasive pad in use of a chemical mechanical polishing process. The method includes: forming one or more etching molds providing a plurality of different real contact areas; attaching the etching mold(s) to a roller or press; and forming a fixed abrasive pad using the roller or press, The fixed abrasive pad has a plurality of polishing portions, each having a different real contact area. Especially, the fixed abrasive pad can comprise a low-density polishing portion having a real contact area less than 20% and a high-density polishing portion having a real contact area of 20%-50%.

This application claims the benefit of Korean Application No.10-2005-0061837, filed on Jul. 8, 2005, which is incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fixed abrasive pad and fabricationmethod thereof. More specifically, the present method relates to a fixedabrasive pad having different real contact areas in use in a chemicalmechanical polishing (CMP) process, and a method for forming differentreal contact areas on a fixed abrasive pad.

2. Description of the Related Art

There have been a variety of alterations in structural and materialaspects for the purpose of achieving a higher operational speed andintegration of a semiconductor device. In the structural aspect, thenumber of metallization layers has been increased, and a shallow trenchisolation (STI) technique has been employed. In the material aspect,copper (Cu) has been used as a metallization layer, and a low-kinsulating material has been used as an interlevel dielectric. A CMPprocess has been frequently employed according to such alterations.

FIG. 1 shows conventional equipment for a CMP process.

Referring to FIG. 1, the conventional CMP equipment comprises: a turntable which is rotated, with a polishing pad 21 mounted thereon; a wafercarrier 10 which transfers a wafer W according to processing sequencesand rotates the wafer while it is in contact with the polishing pad 21;a polishing slurry supplier 40 over the turn table 20, supplying aslurry to the polishing pad 21; and a diamond dresser 30. In suchstructured CMP equipment, the wafer W is positioned on the polishing pad21, and simultaneously forced downwardly by the wafer carrier 10.According to rotation of the turn table 20 and continuous supply of theslurry solution, a material of the wafer is removed or polishedmechanically by friction between the polishing pad 21 and thesemiconductor wafer W, and chemically by chemical ingredients of thepolishing slurry.

The above-described CMP process has been widely used as a planarizationprocess of metallization layers, however, the CMP process often resultsin a problem where the yield of semiconductor devices decreases due tofailures such as a dishing or erosion phenomenon.

In order to reduce or eliminate dishing and erosion phenomena, recentlyimproved CMP process involves using a high selectivity slurry, formingdummy patterns on a chip, or using a reverse etch technique. Inaddition, because the dishing and erosion phenomena occur ultimately dueto the polishing pad in the CMP process, a polishing method utilizing afixed abrasive pad instead of a slurry has been developed and ispartially applied, wherein the fixed abrasive pad includes abrasiveparticles adhering to a pad.

A method for fabricating a fixed abrasive pad involves applying amixture of abrasive particles, a binding agent, and a hardening agent ona polycarbonate film, and then forming a polishing pad using a roller ofwhich the surface has the shape opposite or complementary to a desiredshape to be formed in the polishing pad. In one case, the roller may befabricated using a cutting tool. However, fabricating a roller by acutting tool consumes a relatively large working time, and may alsodisable or disfigure the minute surface topology of the roller. Thus, inother cases, the roller may have a uniform surface topology so that thepolishing pad fabricated by the roller has a uniform real contact areain a pad.

In general, a fixed abrasive pad has a uniform surface topology,resulting in a wide difference between polishing rates of wafers withand without predetermined patterns. Therefore, different polishing padsmay be separately used for wafers with and without patterns. As aresult, two different CMP apparatuses or equipment are necessary tosimultaneously polish wafers with and without patterns, which is notdesirable in the aspect of processing efficiency and/or efficient use offab/clean room floor space.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a fixedabrasive pad comprising a plurality of polishing portions or areas inone pad. In use of a fixed abrasive pad according to the presentinvention, a wafer with a predetermined pattern is initially polished ona low real contact area (or low contact polishing portion) of the fixedabrasive pad. After polishing the patterned region of the wafer, thewafer is additionally polished on a high real contact area (or highcontact polishing portion) of the fixed abrasive pad. Thereby, it canreduce or prevent adverse effects due to variations in removal ratesaccording to the surface morphology of the wafer in a CMP process.

To achieve the above object, an embodiment of a method for fabricating afixed abrasive pad in use of a chemical mechanical polishing processaccording to the present invention, comprises the steps of: forming aplurality of etching molds, each etching mold having a different realcontact area from another; attaching the plurality of etching molds to aroller; forming a fixed abrasive pad using the roller; wherein the fixedabrasive pad comprises a plurality of polishing portions in one pad, andeach polishing portion has a different real contact area from another.Here, the roller can comprise a plurality of through-holes whereby avacuum is applied, and the plurality of etching molds are attached tothe roller by a vacuum absorption mechanism. Especially, the fixedabrasive pad can comprise a low-density polishing portion having a realcontact area less than 20% and a high-density polishing portion having areal contact area of 20%-50%.

In addition, a method for fabricating a fixed abrasive pad in use of achemical mechanical polishing process, can comprise the steps of:forming a plurality of etching molds, each etching mold having adifferent real contact area from another; attaching the plurality ofetching molds to a press; and forming a fixed abrasive pad using thepress. Here, the fixed abrasive pad can comprise a plurality ofpolishing portions in one pad, and each polishing portion has adifferent real contact area from another.

These and other aspects of the invention will become evident byreference to the following description of the invention, often referringto the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating conventional CMPequipment.

FIG. 2 shows a graph illustrating variation in normalized RR ratioaccording to a real contact area of a polishing pad.

FIG. 3 is a photograph illustrating an etching mold according to anembodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a method for fabricating afixed abrasive pad according to a first embodiment of the presentinvention.

FIG. 5 is a perspective view illustrating a roller includingthrough-holes, according to the first embodiment of the presentinvention.

FIG. 6 is a plane view illustrating the state that etching molds havingdifferent real contact areas are attached on the roller according to thefirst embodiment of the present invention.

FIG. 7 is a cross-sectional view illustrating a method for fabricating afixed abrasive pad according to a second embodiment of the presentinvention.

FIG. 8 is a photograph illustrating a fixed abrasive pad fabricatedaccording to the embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows a graph illustrating a variation in normalized RR ratio,representing a ratio of a real removal rate (real RR) to a mean orreference removal rate (reference RR), according to a real contact areaof a polishing pad. In the context of the present invention, “realcontact area” may refer to the average surface areas of the abrasiveparticles in the fixed abrasive pad and the wafer that actually comeinto contact with each other under predetermined polishing conditions.

Referring to FIG. 2, there is a wide difference between RR ratiosaccording to the real contact area. For a given wafer (e.g., a waferhaving a relatively high density of patterned features), the normalizedRR for a pad or pad region having a 30% real contact area can be abouttwo, relative to a polishing pad having a 10% real contact area. A waferhaving patterns, or at least one region with a relatively high densityof patterned features, for example, may have patterned features of awidth (or minimum dimension) of from about 90 nm to about 1 μm and aninter-feature spacing of from about 125 nm to about 2 μm, over an areacontaining at least 4 (and, in some embodiments, at least 8, 16 or 30)such features.

In the case where a wafer with patterns is polished, using a fixedabrasive pad having different real contact areas in one pad can preventdeterioration of the removal rate according to a real contact area of apolishing pad. In such case, a patterned region of a wafer is initiallypolished on the region of the polishing pad that has a low real contactarea. After initial polishing of the patterned wafer is finished, thewafer is additionally polished on the region of the polishing pad thathas a high real contact area. Accordingly, the wafer with patterns canbe polished using one pad, thus decreasing the total processing time andimproving efficiency of the CMP equipment (in terms of throughput and/orclean room floor space).

Hereinafter, a method for fabricating a fixed abrasive pad havingdifferent real contact areas in one pad will be described.

A First Embodiment

Firstly, an etching mold is formed, having a surface morphology oppositeor complementary to the shape that is desired on a surface (e.g., thepolishing surface) of the polishing pad. An exemplary etching mold isshown in FIG. 3. A metal material such as stainless steel is etchedusing a metal etching technique to form the mold, such as that shown inFIG. 3. The etching molds may be formed in at least two separate pieces,wherein one etching mold provides a polishing pad or pad region that hasa different real contact area from another polishing pad or pad region.Alternatively, the mold may be formed in one unitary piece.

Next, the etching mold(s) providing different real contact areas areattached to a surface of roller. Preferably, the roller includesthrough-holes whereby a vacuum can be applied (e.g., to the inside ofthe roller), and the etching molds may be attached to the surface of theroller by a vacuum absorption mechanism.

A fixed abrasive pad can be formed using the roller provided with theetching molds providing different real contact areas on the surfacethereof.

FIG. 4 shows a first embodiment of a method for fabricating a fixedabrasive pad according to the present invention.

Referring to FIG. 4, a mixture of abrasive particles (which may have apredetermined, relatively uniform particle size distribution and/or arelatively uniform shape), a binding agent, and (optionally) a hardeningagent is applied onto a base of the fixed abrasive pad (e.g., apolycarbonate film or other relatively stiff film capable of havingparticles fixed thereto and withstanding typical wafer polishingconditions). The particles may comprise any known particles for suchfixed abrasive pads, such as alumina, silica, ceria, aluminosilicates,silicon carbide, or other ceramics). Then, the polishing pad is formedby a rolling method using the roller 135. Here, the roller 135 comprisesthe etching molds having the surface morphology opposite orcomplementary to the shape to be formed on the polishing pad, whichapplies pressure to the polishing pad base (supplied by one of therollers on the left-hand side of FIG. 4) and the abrasive particlemixture (supplied by the other of the rollers on the left-hand side ofFIG. 4 [preferably the lower roller], and which may be partiallyhardened by the time it is applied to the polishing pad base and/orpressure-bonded to the base by roller 135) and which may receive agas-based heat and/or drying treatment applied thereto (see, e.g., theheat and/or gas source located below roller 135 in FIG. 4). In oneembodiment, the abrasive particle mixture is applied directly to thebase, and a protective film is placed between the abrasive particlemixture and the roller as the roller applies pressure to the abrasiveparticle mixture applied onto the base.

FIG. 5 shows the surface of roller 135 including through-holes 137thereon, and FIG. 6 shows a layout diagram of the etching molds havingdifferent real contact areas respectively attached to (or prior toattachment to) the roller 135, according to the present invention.

Referring to FIG. 6, a low-density etching mold 140 having a realcontact area equal to or less than 20% and a high-density etching mold145 having a real contact area of 20%-50% are respectively attached tothe roller 136.

A Second Embodiment

The second embodiment of a method for fabricating a fixed abrasive padhaving different real contact areas utilizes a press.

Firstly, a mixture of abrasive particles, a binding agent, and(optionally) a hardening agent is applied on a polycarbonate filmconstituting a base of the fixed abrasive pad, and then a polishing filmis formed by a rolling method using a roller. Here, the roller has nosurface morphology, and the polishing film is temporarily hardened in aconstant thickness. Next, the etching molds having different realcontact areas are respectively attached to a press.

Subsequently, the temporarily hardened polishing film is positioned onthe press, and then is pressed or deformed by the press under apredetermined heat and pressure. After then, the polishing film iscooled, thus forming a fixed abrasive pad having one or more regions ofrelatively low real contact area and one or more regions of relativelyhigh real contact area.

FIG. 7 illustrates a method for fabricating a fixed abrasive padaccording to the second embodiment.

Referring to FIG. 7, the polishing film 153 temporarily hardened by theroller 151 in a constant thickness is pressed and deformed by the press155 on which the etching molds 157 are attached. Here, the etching moldscomprise a low-density etching mold providing a real contact area lessthan 20% and a high-density etching mold providing a real contact areaof 20%-50%.

FIG. 8 shows a fixed abrasive pad fabricated by the present method.

Referring to FIG. 8, a low-density polishing portion having a realcontact of about 10% and a high-density polishing portion having a realcontact area of about 40% are formed on one pad.

According to the present invention, a wafer with patterns can bepolished using one polishing pad, thus enabling reduction of aprocessing time and improvement of efficiency of a CMP equipment.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A method for fabricating a fixed abrasive pad, comprising the stepsof: forming one or more etching molds having a first region providing arelatively low real contact area and a second region providing arelatively high real contact area; attaching the etching mold(s) to aroller; and forming the fixed abrasive pad using the roller, wherein thefixed abrasive pad comprises a plurality of polishing portions in onepad, each polishing portion having a different real contact area fromanother.
 2. The method of claim 1, wherein the fixed abrasive padcomprises a low-density polishing portion having a real contact area ofless than 20% and a high-density polishing portion having a real contactarea of 20%-50%.
 3. The method of claim 1, wherein the roller comprisesa plurality of through-holes, and the attaching the etching mold(s)comprises vacuum absorbing the etching mold(s) to the roller.
 4. Themethod of claim 1, comprising forming a plurality of etching molds, eachetching mold providing a different real contact area.
 5. The method ofclaim 1, wherein the fixed abrasive pad is adapted for chemicalmechanical polishing a wafer using chemical mechanical polishingequipment.
 6. A method for fabricating a fixed abrasive pad, comprisingthe steps of: forming one or more etching molds, having a first regionproviding a relatively low real contact area and a second regionproviding a relatively high real contact area; attaching the etchingmold(s) to a press; and forming a fixed abrasive pad using the press,wherein the fixed abrasive pad comprises a plurality of polishingportions in one pad, and each polishing portion has a different realcontact area from another.
 7. The method of claim 6, wherein the fixedabrasive pad comprises a low-density polishing portion having a realcontact area of less than 20% and a high-density polishing portionhaving a real contact area of 20%-50%.
 8. The method of claim 6,comprising forming a plurality of etching molds, each etching moldproviding a different real contact area.
 9. The method of claim 6,wherein the fixed abrasive pad is adapted for chemical mechanicalpolishing a wafer using chemical mechanical polishing equipment.
 10. Afixed abrasive pad, comprising a first polishing portion having arelatively low real contact area and a second region having a relativelyhigh real contact area.
 11. The fixed abrasive pad of claim 10, whereinthe low-density polishing portion has a real contact area of less than20% and the high-density polishing portion has a real contact area of20%-50%.
 12. The fixed abrasive pad of claim 10, adapted for chemicalmechanical polishing a wafer using chemical mechanical polishingequipment.
 13. A method for polishing a wafer, comprising the steps of:polishing the wafer on a first polishing portion of a fixed abrasive padcomprising a plurality of polishing portions, the first polishingportion having a relatively low real contact area; and polishing thewafer on a second polishing portion of the fixed abrasive pad, thesecond polishing portion having a relatively high real contact area. 14.The method of claim 13, wherein the first polishing portion has a realcontact area of less than 20% and the second polishing portion has areal contact area of 20%-50%.
 15. The method of claim 13, wherein thewafer has a predetermined pattern thereon.
 16. The method of claim 13,wherein polishing the wafer on the second polishing portion occurs afterfinishing polishing the wafer on the first polishing portion.
 17. Apolishing apparatus, comprising: a turn table; a fixed abrasive pad onthe turn table, comprising a first polishing portion having a relativelylow real contact area and a second region having a relatively high realcontact area; and a wafer carrier adapted to hold a wafer and rotate thewafer against the fixed abrasive pad.
 18. The apparatus of claim 15,further comprising a chemical supplier over the turn table.
 19. Theapparatus of claim 15, wherein the first polishing portion has a realcontact area of less than 20% and the second polishing portion has areal contact area of 20% 50%.
 20. An apparatus for making a fixedabrasive pad, comprising: one or more etching molds having a firstregion providing a relatively low real contact area and a second regionproviding a relatively high real contact area; a roller or press towhich the etching mold(s) are attached, adapted to press an abrasiveparticle mixture onto a pad base; and one or more mechanisms forsupplying the pad base and the abrasive particle mixture to the rolleror press.